Cytochrome P450 (cyto P450) is a heterogeneous family of isozymes, is inducible and undergoes ontogenetic changes in rat liver. The hemoprotein plays an important role, both in the activation of protoxins to toxins and in the detoxification of other agents. The administration to rats of 3-methylcholanthrene (MC) induces cytochromes P450c and P450d in rat liver; isosafrole treatment yields predominantly cytochrome P450d. The long-range goal of the laboratory is to understand the details of the regulation of this system by environmental substances, e.g., polycyclic hydrocarbons, and by isosafrole. This understanding is necessary to allow this system to be better exploited as a target in toxicology. The specific aims of the proposal are to: a) develop gene specific probes for cytochromes P450c and P450d, b) determine the amount of cyto P450 mRNA (mRNA-p450) present in rat liver as a function of ontogeny, c) determine if structural alterations occur in the chromatin in respect to the cyto P450c and P450d genes as a function of ontogeny, and d) define the sequences of cyto P450c and P450d genes that are involved in the regulation of expression of the proteins as well as the nature of the acceptor sites in chromatin that are responsible for interacting with a cytosolic binding protein. In these studies of environmental concern, we will utilize molecular biological probes (most of which are already on hand), hybridization techniques, and techniques for establishment of the presence of promoter and enhancer elements. These studies would significantly increase our knowledge of a most important rate-limiting system in the activation and inactivation of environmental toxic agents.